I am installing 4 more dedicated circuits for a customer's Christmas lights. Because of the distance, I'd like to use MWBC's. Is there any negative effect of using a 2-pole GFCI breaker as opposed to 2 single pole units? Cost is not an issue here. (They already have 14 circuits) I am using a copper-bussed Siemens panel and #12 Romex if it matters any.

 

Someone feel free to tell me I'm on drugs here but...

I want to say no because the GFCI wants to see the same current on both the hot and neutral, and if two receptacles with two different loads are sharing that neutral, these values potentially will not match and trip the GFCI.

 

That is the reason for using a 2-pole unit.

 

Again, somebody else accuse me of drug use if need be....

Single or double doesn't matter, you are risking nuisance tripping because the breaker or breakers would detect a false fault.

 

yes it will work just fine. I have a sub panel setup that uses a double pole 50 amp GFCI breaker and there is no nuscience tripping when using individual 120 volt loads from the subpanel. the breaker would only sense if there were an imbalance between the hot and neutral, the double pole breaker is designed to continually monitor both hot legs and the neutral and if any leakage occurs to ground or any other path then it will trip

 

I`ll take that as an underlying accusation of being on drugs.
I retract my previous statements and agree with jon.

 

The only downfall I can see is if you have a ground fault on one circuit..... you'll lose them both.